Mineral from a mine has a varied granulometry, with particle sizes ranging from less than 1 mm to fragments larger than 1 m in diameter, and therefore the object of crushing is to reduce the fragment size to obtain a uniform size in which usually 100% is under eight inches in diameter.
Crushers are large electric equipments specialized in crushing the mineral rocks. Transport devices discharge the mineral in the top section of these crushers; while the crushed mineral is collected in the bottom discharge, 100% of them being under 20 cm (8 inches), which is sent downstream to a concentrator to be subjected to a grinding process.
When an uncrushable element enters into the crusher, the crusher will not be able to triturate said element, and this will cause a mechanical jam that will force the crusher to be stopped, and so all the mineral discharge and crushing process must also be stopped.
This problem has no direct solution. Usually, a traditional solution to detect metallic pieces, if they include ferromagnetic metals, is to set up an electromagnet over a conveyor belt that carries the material to be processed. For example, Zhengzhou Jinding Heavy Industry Co. Ltd. supplies equipment for the mining industry, metallurgy and any other processes, in which easily attractable ferromagnetic materials can be detected; in these cases, the equipment is installed over the conveyor belts that transport the material and a magnet attracts the metallic pieces and drags them to a waste storage deposit. Other models are also available (Zhengzhou Jinding Heavy Industry Co., Ltd), known as magnetic ore separators, and some of them are protected by patents, such as the U.S. Pat. No. 3,966,590—Magnetic ore separator and U.S. Pat. No. 1,729,095—Electromagnetic ore separator. However, these solutions cannot be applied to any transport devices that transports materials to primary crushers, since in some cases mineral rocks and rock fragments are loaded in especially reinforced large capacity mining dumper trucks or train cars. Additionally, many metallic pieces are made of austenitic steel and therefore cannot be removed by electromagnets.
Currently, solutions to minimize this problem have been designed, based in the use of video cameras to detect the fall of teeth of a mechanical shovel that loads a mineral transport truck.
Variants of the same solution incorporate lasers to illuminate the inspection zone monitored by the video cameras, with additional mobile elements to carry out the laser scan or using a line projecting laser. These devices operate in the visible or near infrared (NIR) range and present a low degree of efficacy because of the environmental contamination by dust, which have a particle size in the range of the emission wavelength of the lasers. The company HighService discloses in its website (http://www.highservice.cl, Sep. 30, 2009) a system of this type to prevent mechanical shovel hopper teeth and/or adapters to damage primary crushers and cause production losses. The system detects these materials through digital image processing, wherein the scene is illuminated by a line laser operating in the near infrared spectrum. The operator cabin interface automatically informs the operator if the fall of a tooth or adapter is detected, the operator checks the hopper and then confirms the event.
Other applications use the Laser Range Sensing (LRS) technology to construct a 3D image from the signals, which is compared to the CAD design of the shovel onto which the equipment is installed. If differences are detected, an alert signal is delivered to the shovel operator. An experiment was published in 2004, using a prototype to detect the loss of teeth of extracting mechanical shovels by means of a laser (Laser Rangefinder AR4000, manufactured by Acuity Research) (X. Luo, H, Zhang: Missing tooth detection with laser range sensing, Proceedings of the 5th World Congress on Intelligent Control and Automation, Jun. 15-19, 2004, China).
The detection systems of the previous art, based in digital image processing, i.e., optical systems, are oriented to detect the fall of teeth from a mechanical shovel that loads a mineral transport truck, but these systems have a number of inconveniences. The detection systems must be installed onto the shovel, which requires one optical system per shovel, the detection systems have a low detection efficiency because the optical components of the systems can be contaminated by environmental dust and become blind, and the detection systems require complementary illumination equipments because they do not operate with low illumination levels.
All these applications aim to solve the problem installing a detection system right on the shovel. However, even when the fall of an teeth element of the shovel is detected, the exact falling location of said element is not known, which forces the transport device to be put off track and to deposit the load in other location, with no indication whether the uncrushable element has been lost in the process or not. Furthermore, there are other metallic pieces coming from other process operations which are hidden among the load material and can likewise arrive to the crusher.
One of the most important operations in a mining operation is primary crushing. After extraction, the mineral is transported to the crushers using the transport device, typically large capacity trucks or cargo train cars. During operation, it is not unusual that an uncrushable metal piece, e.g., a tooth of the shovel that loads the transport device, is transported together with the mineral load.
The entrance of a hard element into a primary crusher can cause, depending on its size, a jam and a subsequent unscheduled stop of the crushing equipment for several hours, which brings along production losses and generates maintenance and repair costs. To solve this problem, the presence of uncrushable elements in the mineral must be detected in good timing (before the mineral is discharged into the primary crusher).
One part of the efforts to solve the problem has been oriented to prevent certain types of uncrushable elements, such as shovel teeth, to enter into the primary crusher, using video cameras and image processing technology, lasers combined with image processing, etc., which are technologies oriented to detect the fall of a tooth or adapter into a shovel. However, there have been cases in which, even though the fall of a shovel tooth has been detected, the tooth was found in the crusher several hours later. The previous problem is aggravated by the fact that diverse uncrushable metallic pieces (perforation tricones, steel bars and other metal pieces), coming from other stages of the mineral extraction process, have also been found in crushers.